Effects Of Earthworms On The Ecological Improvement Of Cover Soil On Coal Gangue Pile

China is a country with a large output of coal gangue.According to statistics,90 million tons of coal gangue are discharged annually in China,accounting for 10-20%of coal output.A large number of coal gangue piled up on the surface will cause great harm to the environment,and the ecological restoration of the gangue piles will reduce its harm to the environment.In the ecological restoration of coal gangue dump,the physical and chemical properties and fertility level of overlying soil can have a greater impact on plant growth.Many studies have shown that earthworms can produce certain ecological functions on Soil and phytoremediation plants.Therefore,this study intends to simulate the ecological environment of the waste dump through laboratory microcosmic experiments.Based on the symbiotic experiments of earthworms and plants in the overlying soil with different thickness on the waste dump,through the analysis and testing of the physical and chemical properties of the overlying soil,the content of heavy metals and the content of available state in the soil,it is intended to reveal the improvement effect of earthworms on the overlying soil.At the same time,combined with the addition of earthworms,the plant growth potential and the activity of plant resistance enzymes in the overlying soil were analyzed to clarify the regulation of earthworms on plant growth.Finally,the function of earthworms in the ecological restoration of coal gangue hills was explored.Through the experimental research,the main conclusions are as follows:(1)Earthworm activity can significantly change the physical and chemical properties of overlying soil..The thickness of overlying soil has different effects on soil pH,organic matter,total N,total P and total K.Earthworms can reduce soil pH in different thickness of covering soil,and when the thickness of covering soil is 10 cm,the ability of reducing soil pH is the greatest;earthworms can increase the content of organic matter in different thickness of covering soil,and increase the content of organic matter in 30cm;Similarly,after earthworms are put,the content of total N,total P and total K of covering soil increases,respectively,in the thickness of 30 cm,30 cm,50 cm,50 cm,50 cm,respectively.Maximum at cm.(2)Earthworm activity can significantly change the concentration of elements in overlying soil.Through the analysis of element concentration in mulched soil for 7 days,21 days and 40 days,it was found that earthworms could reduce the concentration of heavy metals(Cr,Cu,Pb,and Zn)in soil.The change of element concentration in the overlying soil is also different with the thickness of the overlying soil.When the cover thickness is 50 cm,earthworms have the greatest ability to reduce the concentration of Cr,Pb and Zn;when the cover thickness is 70 cm,earthworms have the greatest ability to reduce the concentration of Cu;with the increase of time,the concentration of heavy metals in the cover soil also decreases,and the concentration of heavy metals decreases more obviously in 7-21 days.Earthworms can also increase the DTPA content of heavy metals in soil,and the effect is best when the cover thickness is 50 cm.(3)Earthworm activity can significantly change the growth state of plants in overlying soil.After earthworms were added,plant length and fresh weight of the upper and underground parts of vetiver grass increased,and the growth of vetiver grass was the best in 50 cm and 70 cm soil cover thickness.After earthworms were added,the contents of SOD,POD and CAT in Vetiver Grass increased,and with the increase of soil cover thickness,the activity of enzyme increased,reaching the maximum at 50 cm soil cover thickness;the content of proline and soluble protease increased with the increase of soil cover thickness.MDA and chlorophyll increased with the increase of overlying soil thickness,and reached the maximum at 50 cm and 70 cm.Therefore,putting earthworms into the overlying soil of gangue hill can really improve the nature of the overlying soil and change the growth of plants.Overall,earthworms can play the largest ecological improvement effect in the 50 cm to 70 cm soil cover.This study shows that earthworms can play a good ecological function in the ecological restoration of gangue hills.